The present description relates to an oil separator to separate oil contents from blow-by gases of an internal combustion engine, and particularly relates to an oil separator which is arranged on a cylinder head of the engine.
When an air-fuel mixture is combusted in the engine combustion chamber, a small portion of the combusted gas may go into the engine crankcase through the piston rings. This is referred to as blow-by gas, but it is essentially engine exhaust gas. Therefore, the gas needs to be prevented from going out directly to the atmosphere. Thus, for example, by communicating the crankcase with the engine intake system at a lower pressure, the blow-by gas is caused to flow from the crankcase to the engine intake system and caused to be mixed with fresh air. Then, it is inducted into the combustion chamber for re-combustion.
Engine lubrication oil is supplied into the crankcase at a higher pressure for lubricating moving parts. That higher pressure causes some of the supplied oil to be in a mist form in the crankcase. The oil mist may mix with the blow-by gas. If the blow-by gas containing the oil mist is returned to the intake system, the oil content may be combusted in the combustion chamber. This may cause the oil consumption to increase, or it may cause disadvantageous effects on the engine exhaust system.
An oil separator is disclosed, for example, in Japanese Patent Application Publication JP2003-301710A to separate oil content from the blow-by gas containing the oil mist. When the blow-by gases flow through a bending passage made with baffles, for example, a difference of kinetic energies between gases and liquids separates the liquid form of the oil content from the blow-by gas containing the oil mist. The oil content is returned to the engine lubricating system, and the blow-by gas is returned to the engine intake system as described above.
An oil separator chamber disclosed in the '710 publication is arranged in a valve drive chamber defined between a cylinder head and a head cover. The valve drive chamber is in fluid communication with the crankcase and the intake system so that the blow-by gas may flow from the crank case to the intake system. A camshaft and other moving parts are lubricated with the engine oil in the valve chamber. Therefore, the gas in the valve drive chamber may contain more of the oil content even though some of the oil content has been separated from the gas during the course of flow from the crankcase to the valve drive chamber. To sufficiently separate the oil content from the blow-by gas in the valve drive chamber, the oil separator chamber of the '710 publication has a gas communication opening for communicating with the valve drive chamber at its one end and another opening to the intake system at the opposite end, thereby maximizing the oil separator passage length.
For example, when the engine is used for a vehicle, such as an automotive vehicle, the engine size is required to be smaller for package constraints of an engine room. For this requirement, the communication opening of the oil separator chamber may be located closer to the camshaft. In the valve drive chamber, the camshaft rotates and splashes the oil. Due to the closer distance between the communication opening and the camshaft, the splashed oil may go into the oil separator chamber through the communication opening. At the same time, the blow-by gas may flow through the communication chamber, and some of the splashed oil may mix with the blow-by gas. Consequently, the oil concentration in the blow-by gas may increase, and degrade the oil separator performance.